Eclipse in corner country

Having studied the solar corona and its radio emissions sunspot cycles ago, I was keen to verify its existence optically during the total solar eclipse of Wednesday, 4 December 2002, the first on Australian soil since 1976. The moon's shadow was to travel from the south-Atlantic west of The Congo, across southern Africa, the Indian Ocean and into the Great Australian Bight, finally making Australian landfall at Ceduna, South Australia (SA). The umbra was to move across south-east SA, clip the north-west corner of New South Wales ("corner country") and leave the Earth's limb west of Bulloo Downs in south-west Queensland. The favoured site to observe the eclipse was Ceduna. However, Ceduna is a longish drive (2200 km), whereas the New South Wales portion of the path is a mere 1300 km from the ATNF headquarters in Sydney.

Near the end of the track the eclipse path was just under 30 km wide, with Cameron Corner five km from its northern edge. The excellent publication by Fred Espenak and Jay Anderson (Total Solar Eclipse of 2002, 04 December 2001) told us that in this region the eclipse would be two degrees above the horizon and the duration of the total phase would be only 22 seconds on the centre line of the umbral path.

About three weeks before the eclipse date I approached my long-time friend and colleague, the incomparable Dr Jon Ables, with a view to forming an eclipse team. Just prior to departure at 11:30 on Monday, I was approached by Lister Staveley-Smith. He also intended to watch the eclipse. Did I know anything about getting to Cameron Corner? Lister decided to find a co-driver and leave Sydney early on Tuesday morning in time to meet us for the eclipse on Wednesday afternoon.

On the first day, we covered mainly familiar country and made camp on the Mitchell Highway beyond Dubbo, between Trangie and Nevertire. The road is very straight with few bends on the 330 km from Narromine to Bourke. We arrived in Bourke at 10:30 the next day - the temperature was already 38 C. The road is sealed for about 10 km out of Bourke and the other 400 km is red sand, bull dust or gravel. The heat was hot, the sky overcast. We reached the Mt Wood camp ground in the SE corner of the Sturt National Park at about 18:30.

Overnight, on eclipse day, the weather changed. The sun appeared at sunrise but quickly passed behind the clouds that covered the eastern sky. During the morning the clouds thinned out and broke up. We drove 25 km to Tibooburra. Tibooburra is an aboriginal word for "heap of rocks" - an apt description. Cameron Corner is 140 km from Tibooburra. The country is surprisingly variable with gibber plains, "jump ups", clay pans and finally, beyond Waka, dunes of red sand. The road crosses the centre line of the umbral track just south of the Fortville Gate, 22 km east of the Corner. The gate is one of many allowing passage through the fence that runs around NSW along the SA and Qld borders. Evidently the fence was originally built to keep rabbits out of SA, but now keeps dingoes out of sheep grazing areas. It is said to be the world's longest fence - 5614 km.

In the area of the intersection between road and umbral centre-line we chose a tree that cast a shadow larger than us and our lunch. With the aid of Jon's GPS receiver, Fred's tables and my map of Sturt National Park, we calculated our location to be about 500 m south of the centre line. The sky became absolutely cloudless. The country here has series of parallel red sand dunes, arranged at an angle to the direction of the setting sun. The dunes are around 400 m apart. We had to choose a site with the western horizon unobscured by either nearby scrub or by the next dune. We decided to select a position on the sunward side of a dune, out of the thicker scrub, and have our sight line across the clear inter-dune area, and still fairly distant from the ridge of the next dune. Lister and co-driver Jenn Donley joined us at about 16:30. Jenn is a Fullbright Scholar working at the ATNF with Lister and is studying galaxies behind the "Zone of Avoidance".

Figure 1: The Team

The eclipse shadow travelled from Ceduna to our location in 77 seconds, arriving at 09:11:29 UT (20:11:29 AEDT). First contact began just before 19:15. We had come prepared with "eclipse glasses" - sunglasses made from specially dense film and cardboard. I had also bought a sheet of "Baader film", a foil that transmits only 10^-5 of the incident sunlight. Solar filters were made for camera and binocular lenses. With the help of Fred's tables I selected exposure settings for both the partial phase through the filter, and the total phase without the filter. The other important equipment we had was folding chairs. Being close to the horizon this was an armchair event.

We synchronised watches - with Jon's GPS receiver of course. We saw first contact within seconds of the predicted time. We watched as the moon glided upwards across the sun's face, starting just to the left of the lower limb. We had 57 minutes of partial phase giving plenty of time to take photos and check cameras. We noted the changes to shadows as the sun changed shape. We made a number of impromptu pin-hole cameras in a flurry of optical experimentation. As the sun slipped away the lighting took on that wierd quality only seen when it comes from a narrow crescent. The temperature had been 32 C all afternoon; we noticed a four-degree drop during the partial phase. Just minutes before totality "all the animals acted strange". Well, a pair of budgerigars flew by looking irritated, and the humans had been acting strangely all day.

We counted out the last few seconds, removed our eclipse glasses and filtered binoculars and there it was. BRILLIANT! No photographs prepare you for the sight of the solar corona. The range of brightness is far more than can be recorded on film - very bright close to the lunar limb and fading away but still visible at a great distance. I found the colour quite unexpected. Lister's description of pearly white is close. The brilliance and extent of the corona gave it a shimmering appearance. And then it passed.

Figure 2: The south-western horizon

We were all "first timers". We were all stoked. It was well worth the 1300 km drive for 22 seconds of one of nature's rarer displays. We slept under the stars. No dew, no insects, just thousands of stars. Around two in the morning the sky was dark, stars wheeled silently above and a desert thorn made its way through Jon's ground sheet and deflated his air mattress.

David McConnell
(David.McConnell@csiro.au)